GeoDataset performance

[calebrob6]

We have benchmark.py for evaluating the performance of different sampler methods over a GeoDataset. Currently benchmark.py works with a ZipDataset of Landsat 8 imagery and CDL labels. Generally, we want TorchGeo to be able to sample arbitrary patches of data from GeoDatasets as quickly as possible.

There are several GeoDatasets cases that we need to consider:

• When both reprojection and resampling need to be done
• When only resampling needs to be done
• When neither needs to be done

This issue is to track the performance of these cases.

[adamjstewart]

Also see #81 for a lot more things to consider.